1. Field of Invention
This invention pertains to a self-propelled wheelchair. More particularly, this invention pertains to a self-propelled wheelchair having independently driven wheels and an articulated support frame.
2. Description of the Related Art
Self-propelled wheelchairs having one or more front wheel drive motors and/or rear wheel drive motors are typically utilized for travel across generally level surfaces. Wheelchairs having multiple motors for simultaneously rotating front wheels and rear wheels are typically designed with the front wheels, or the rear wheels, having a steering mechanism which is controlled by an operator's input to a ‘joystick’ control device in order to direct the front pair or rear pair of wheels in a selected direction for wheelchair movement.
An example of a multiple motor wheelchair having four electric motors is disclosed in U.S. Pat. No. 4,805,712, issued to Singleton. The multiple motor wheelchair includes an electric motor for driving each respective wheel, and includes a steering linkage having an electric actuator for turning the front wheels in response to manipulation of a joystick by the operator. The multiple motor wheelchair utilizes a rigid frame to which each wheel is rotatably attached, and to which the electric actuator is secured. The rigid frame does not include an articulating portion, therefore the rear wheels follow generally the same track as the front wheels, and the rear wheels rotate in the same direction as the front wheels during wheelchair movement. The turning radius of the multiple motor wheelchair is delineated by a turning angle created by the extension or retraction of the electric actuator connecting to the front wheels which simultaneous steers both front wheels when the electric actuator is activated by the operator.
An example of a wheelchair having an articulated pivot assembly is disclosed in U.S. Pat. No. 4,633,962, issued to Cox et al. The wheelchair includes front and rear sections pivotably connected at an articulated pivot assembly disposed forward of an occupant's seating position which centers the occupant's weight above the rear drive axle and rear wheel drive motor. The wheelchair is guided by a steering wheel mechanism extended above the wheelchair front section including a solid transverse axle extending between the front wheels. The occupant's seating position is supported by the wheelchair rear section having the driven rear wheels attached, and the occupant's feet are supported by the wheelchair front section having the steering front wheels attached. The occupant steers the wheelchair by turning the steering wheel resulting in turning of the front wheels and resulting in the driven rear wheels following along a path of the front wheels. Therefore, a significant turning radius is required for the wheelchair to negotiate left and right turns.
An improved wheelchair is sought which provides individual motors for independently driving each wheel in order to separately rotate each wheel in appropriate rotational directions and at the same or different rotational speeds thereby allowing rapid and precise turning of the wheelchair as controlled by an operator.
In addition, an improved wheelchair is sought including four wheel drive and providing at least one articulation joint between front and rear support frames having respective front and rear wheels independently driven by separate motors to provide rapid turning of the wheelchair substantially within the footprint formed by the wheelchair.